Honestly, it's different for everyone. Some people feel the Remicade kicking in during the first infusion, and some don't until the 3rd infusion or even later.
That being said, I've been on Remicade for 2 years now, and haven't had any activity in the fistula area.
Check out the Remicade Club thread to read all about other people's experiences with Remi.
I hope it works well for you, good luck!!
MBH